1. Field of the Invention
The present invention generally relates to a cell system, and more particularly, to a fuel cell system.
2. Description of Related Art
Referring to FIG. 1, a conventional direct methanol fuel cell system 100 mainly includes a circulatory device 110, a direct methanol fuel cell module 120 and a methanol-supplying device 130. The direct methanol fuel cell module 120 includes a membrane electrode assembly (MEA) 122, an anode flow field plate 124a, a cathode flow field plate 124b, an anode current-collecting plate 126a and a cathode current-collecting plate 126b. The MEA 122 is located between the anode flow field plate 124a and the cathode flow field plate 124b, the anode flow field plate 124a is located between the anode current-collecting plate 126a and the MEA 122, and the cathode flow field plate 124b is located between the cathode current-collecting plate 126b and the MEA 122. The MEA 122 includes an anode carbon cloth 122a, an anode catalyst layer 122b, a proton exchange membrane (PEM) 122c, a cathode catalyst layer 122d and a cathode carbon cloth 122e, which are sequentially arranged from a side near the anode flow field plate 124a to a side near the cathode flow field plate 124b. The anode flow field plate 124a has an inlet I1 and an outlet O1. The circulatory device 110 is adapted for injecting methanol solution into the anode flow field plate 124a via the inlet I1, and the injected methanol solution permeates from the anode flow field plate 124a through the anode carbon cloth 122a and then be diffused in the anode catalyst layer 122b, where an anode half-reaction is produced as follows:CH3OH+H2O→CO2+6H++6e−The remainder methanol solution after the reaction flows into the circulatory device 110 via the outlet O1.
Similarly, the cathode flow field plate 124b also has an inlet I2 and an outlet O2. The inlet I2 is adapted to make oxygen gas pass there-through and then be injected into the cathode flow field plate 124b. The injected oxygen gas permeates from the cathode flow field plate 124b through the anode carbon cloth 122e and then is diffused in the cathode catalyst layer 122d, where a cathode half-reaction is produced as follows:3/2O2+6H++6e−→3H2OThe electrons produced by the anode half-reaction are delivered to outside from the anode current-collecting plate 126a and return to the cathode current-collecting plate 126b, which forms a loop so as to provide the cathode half-reaction with required electrons. The hydrogen ions produced by the anode half-reaction are driven by an electrical permeability force to penetrate into the cathode catalyst layer 122d via the PEM 122c in a form of a hydrogen ion together with several water molecules, so as to provide the cathode half-reaction with required hydrogen ions. The overall reaction combining the anode half-reaction with the cathode half-reaction is expressed as follows:CH3OH+3/2O2→CO2+2H2O
The water produced by the cathode half-reaction is introduced into the circulatory device 110 via the outlet O2. The remainder methanol solution in the anode half-reaction, the water produced by the cathode half-reaction and the methanol supplied by the methanol-supplying device 130 are mixed up into methanol solution in the circulatory device 110, and the methanol solution is injected into the anode flow field plate 124a via the inlet I1.
The output electrical power of the methanol fuel cell system 100 is related to the temperature of the methanol solution injected to the anode flow field plate 124a via the inlet I1. In general, the higher the temperature of the methanol solution, the higher the output electrical power is. The heat energy produced by the anode half-reaction is able to increase the temperature of the remainder methanol solution after the reaction. However, after the remainder methanol solution is mixed with the water produced by the cathode half-reaction and the methanol supplied by the methanol-supplying device 130 into the methanol solution required by the anode half-reaction and the methanol solution then is conveyed through the whole fluid-conveying path of the circulatory device 110, the temperature of the methanol solution required by the anode half-reaction is largely reduced. Therefore, due to a too low temperature of the methanol solution injected into the anode flow field plate 124a, the output electrical power of the conventional methanol fuel cell system 100 is quite low.
In order to increase the temperature of the methanol solution in the anode flow field plate 124a, some of the conventional methanol fuel cell systems employ an electric heating wire or an electric heater to heat the methanol solution to increase the temperature of the methanol solution, which consumes additional electrical energy and reduces the total output electrical power of the methanol fuel cell system.